Technical Field
The present invention relates to: a composite of silicon oxide nanoparticles and a silsesquioxane polymer and a production method thereof, which are used in the production of a silicon oxide-containing composite cured film having an extremely low refractive index; and an interlayer insulation film, a semiconductor material, an anti-reflection film or an optical material using the same.
Background Art
In the fields of displays and optics, a problem that the visual effects are impaired by reflection of external light at the surface of a display or the like may occur. Thus, it is required that the reflection be reduced by laminating a film having a low or high refractive index on the surface of a display or the like. In order to satisfy such requirement, low-refractive index films having a refractive index close to that of the air have been developed. However, in many cases, the production of such a low-refractive index film requires a large-scale apparatus for chemical vapor deposition and the like, which is disadvantageous from the cost standpoint (for example, Patent Document 1). Therefore, it is desired to develop a material from which a film can be formed by a simple coating method.
Although materials capable of forming a film with a sufficiently low refractive index have been conventionally known, hardly any of them are industrially useful. For example, a fluorine compound-containing material is known (Patent Document 2). However, the cost of the raw material used for introducing a fluorine group into the material is high and, as far as the present inventors know, the effects thereof also have room for improvement. Further, there have been reports on methods of producing mesoporous silica that can be made into a low refractive material by a sol-gel method using an organic spacer decomposable at a low temperature (Patent Documents 3 to 6). Moreover, there are also known methods that use hollow silica particles (Patent Documents 7 and 8). In these methods, a low refractive index is realized by creating pores inside the formed film. However, in these methods that utilize porosity of the formed film, the former methods cannot attain a sufficient reduction in the refractive index without using a large amount of an organic spacer; therefore, it is required that the formation of pores be promoted more efficiently. Meanwhile, the latter methods have room for improvement in that, for example, the particles may undergo secondary aggregation and the surface of the particles must be processed so as to make the particles organic-soluble. From these standpoints, it is desired that particles in an aqueous solvent be reacted as-is because this inhibits secondary aggregation and reduces the processing cost.